1. Field of the Invention
This invention relates to a vapor generating and recovering apparatus for vaporizing a liquid and recovering the vapor, and more particularly to a vapor generating and recovery apparatus providing for continuously moving items to be treated therethrough and recovering virtually all of the generated vapor.
2. Description of the Prior Art
Vapor generating and recovery apparatuses are well known for surface treating objects. The surface treating can be a cleaning treatment wherein foreign material, such as, for example, oil or wax is removed from the surface of the objects, or a heat emitting treatment for shrink fitting or a heat absorbing treatment for reflowing metals. Regardless of the exact nature of the surface treatment, the objects to be surface treated are, typically, immersed into an appropriate treating vapor, and the vapor is recovered for reuse in the treating process.
Examples of such apparatuses are shown in U.S. Pat. Nos. 3,866,307 issued on Feb. 18, 1975 to Pfahl Jr., et. al. and 4,389,797 issued on June 28, 1983 to Spegarelli, et. al. Each of these patents show an apparatus for soldering circuit boards by passing the circuit boards through a hot vapor. The apparatus includes a vessel having heating coils located near the vessel floor. The heating coils are immersed in a liquid to be vaporized and heat the liquid to a temperature at or above its vaporizing temperature.
One example of a heretofore known apparatus is taught in U.S. Pat. No. 3,947,240 issued on Mar. 30, 1976. The apparatus is for generating a vapor for soldering, fusing or brazing articles. The apparatus includes an open topped vessel having a heating coil in the portion end and cooling coils between the top and bottom of the vessel. A eutectic solder heated by the heating coil forms a molten pool over the bottom of the vessel. A liquid to be vaporized forms a pool floating or forming a stratified layer of liquid on top of the molten pool of eutectic solder. The liquid is brought to and maintained at a boil by the heat of the molten solder which acts as a heat transfer medium between the heating coil and the liquid.
In some instances, objects to be surface treated are at a substantially lower temperature than the temperature of the vaporized liquid. When these relatively cold objects are immersed in the vapor, the objects can initially and rapidly absorb enough heat from the treatment vapor to condense this vapor to a liquid. When this happens, the vapor zone collapses. The time required to vaporize the liquid is lost to the treatment process thereby extending the time required to complete the treatment operation. This lost time increases costs, particularly when the treatment process is a step in a high volume manufacturing operation.